Sitagliptin is a triazolopiperazine compound having a beta-amino acid structure and has the chemical name of (2R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro-[1,2,4]triazolo[4,3-α]pyrazin-7(8H)-yl) -1-(2,4,5-trifluorophenyl)butan-2-amine. Sitagliptin was developed by US company, Merck & Co., Inc. Sitagliptin is the first DPP-IV inhibitor to treat type 2 diabetes and is currently commercially available in countries around the world as an antidiabetic drug under the brand name Januvia in the form of a sitagliptin phosphate monohydrate.
The intermediate of sitagliptin “t-butyl (R)-4-(3-(trifluoromethyl)-5,6-dihydro-[1,2,4]triazolo[4,3-α]pyrazin-7(8H)-yl)-1-(2,4, 5-trifluorophenyl)-4-oxobutan-2-ylcarbamate” (Compound 2 in Reaction Scheme 1 below) is prepared as in Reaction Scheme 1 and is disclosed in U.S. Pat. No. 6,699,871.

However, the foregoing method of Reaction Scheme 1 disadvantageously employs expensive reaction reagents, 1-hydroxybenzotriazole (HOBT) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and exhibits a very low product yield. Therefore, this method is not suitable for industrial-scale application.